1. Field of the Invention
This invention is in the field of producing semiconductor luminescence diodes and involves controlled removal of a monocrystal on which has been grown an epitaxial layer and the formation of a pn-junction in the exposed areas.
2. Description of the Prior Art
There are processes for producing semiconductor luminescence diodes which employ a disc-shaped monocrystal as a substrate, the monocrystal usually consisting of a semi-insulating material such as gallium arsenide (GaAs). One surface of the monocrystal has deposited on it a doped mixer crystal layer usually of gallium-aluminum arsenide whose aluminum content reduces with increasing distance from the substrate. This mixed crystal layer forms the actual semiconductor body of the luminescence diode. It must therefore be provided with a pn-junction and the electrodes therefor. A known process of this type is described in the "IEEE Journal of Quantum Electronics", Volume QE-8, No. 3, March 1972, pages 370 and 371.
A typical process for producing such luminescence diodes starts with a solution of gallium arsenide in molten gallium, mixed with a conventional dopant such as tellurium and also containing aluminum. This molten material is brought into contact with a semi-insulating substrate of gallium arsenide at an appropriately high temperature such as 950.degree.C. As a result of a reduction in temperature, crystallization takes place, the crystallized material having a lower aluminum content at increasing distances from the surface. The aluminum gallium arsenide ratio in the melt is usually on the order of 1 to 30 to 1 to 40, in which case the desired epitaxial layer is obtained without difficulty if the substrate is brought into contact with the melt at a temperature of approximately 950.degree.C. When a stationary heat equilibrium has been achieved between the substrate and the melt, the temperature of the seed crystal and the melt is slowly reduced to approximately 900.degree.C. A typical melt may be composed of 3 grams of gallium, 10 milligrams of aluminum and 300 milligrams of gallium arsenide at 960.degree.C.
The epitaxial layer obtained in this manner is monocrystalline. It is also n-conducting. A pn-junction is produced by diffusing in zinc or other acceptor element and utilizing a high doping concentration.